1. Field of the Invention
The present invention relates to a flat picture display device utilizing electron beams.
2. Description of the Prior Art
Examples of a flat picture display device utilizing electron beams, well known in the art, are shown, respectively, in FIGS. 12 and 13 of the accompanying drawings.
In particular, the flat picture display device shown in a FIG. 12 in schematic side sectional representation is disclosed in Japanese Laid-open Patent Publication No. 63-187538, published in 1988. Referring to this figure, positioning members 116 are held in contact with parallel cathode electrode filaments 115 at respective regularly spaced locations so chosen that, in the event that some or all of the cathode electrode filaments 115 may undergo vibration which may constitute a cause for variation in brightness of an image being reproduced, nodes of vibration can lie at respective points of contact between the positioning members 116 and the cathode electrode filaments 115 thereby to minimize the influence which may be brought about by the vibration of the cathode electrode filaments 115 on the image being displayed.
According to the prior art system referred to above, however, in order for the positioning members 116 to be assuredly held in contact with the cathode electrode filaments 115, each of the positioning members 116 must have a precisely machined height, or otherwise an effective suppression of the vibration of the cathode electrode filaments 115 cannot be attained.
In view of this, an attempt has been made to use positioning members which each have an outwardly tapered end against which the cathode electrode filaments 115 are pressed, thereby to minimize the influence which may be brought about by the vibration of some or all of the cathode electrode filaments on the image being displayed. The prior art flat picture display device based on the above mentioned attempt is disclosed in, for example, Japanese Laid-open Patent Publication No. 1-33994, published in 1989, which is reproduced in FIG. 13 in a schematic sectional representation.
Referring now to FIG. 13, the prior art flat picture display device shown therein comprises a faceplate 21 having an inner surface deposited with phosphor material to provide a phosphor screen 22. The picture display device also comprises a back covering 23 which forms an evacuated envelope in cooperation with the faceplate 21. Cathode electrode filaments 24 extending parallel to each other and spaced a predetermined distance from each other are applied to a back electrode 20 in contact therewith, said back electrode 20 being so shaped as to protrude towards the phosphor screen 22. Positioned within the evacuated envelope and held between an electrode retainer 32 and the cathode electrode filaments 24 are electron beam control electrodes 25, 26 and 27 and electrically insulating spacers 28, 29, 30 and 31 which are so disposed as to alternate with the adjacent electron beam control electrodes 25 to 27. Reference numeral 34 designates an electrode support and reference numeral 35 designates an electrode back-up member. The illustrated flat picture display device is so designed and so structured that electron beams 36 emitted from the cathode electrode filaments 24 can travel through the assembly of control electrodes and then impinge upon the phosphor screen 22 to excite phosphor dots on the phosphor screen 22 thereby to emit light.
According to the second mentioned prior art publication, the assembly including the insulating spacers 29 to 31, the electron beam control electrodes 25 to 27 and the back electrode 20, to which a filament-like cathode support member 20a is disposed with the respective cathode filaments 24 interposed between the filament-like cathode support members 20a and the back electrode 20, is so shaped and so curved as to protrude towards the phosphor screen 22 by placing the assembly on a curved spacer 33 and then pressing the assembly against the curved spacer 33 by means of the back-up member 35. The curved spacer 33 provides a base for the shaping of the assembly and, hence, the back electrode 20 originally having a flat shape is curved at the final stage of the shaping process. Since a stack of the alternately disposed insulating spacers 28 to 31 and control electrodes 25 to 27 is interposed between the curved spacer 33 and the back electrode 20, the back electrode 20 will fail to have a smoothly curved shape and will undulate unless the stack of the insulating spacers and the control electrodes is assembled to have a uniform thickness over the entire surface thereof. If the back electrode 20 undulates, some or all of the cathode electrode filaments 24 would be unable to contact the respective filament-like cathode support members 20a uniformly over the entire length thereof and, as a result thereof, an effective elimination of any possible vibration of some or all of the cathode electrode filaments 24 cannot be accomplished.
In addition, in order to retain the curved shape of the assembly, an external force has to be applied uniformly over the entire surface of the curved spacer 33, thereby complicating the structure of the flat picture display device.